While the world continues to be fascinated with the life and works of the late Princess Diana, two of the most important figures in her life are finally opening up about her tragic death. Prince William, Duke of Cambridge, and Prince Harry will sit down on camera to discuss the days following their mother’s death in a new documentary.

NBC will air a two hour examination of the tumultuous week following the death of Diana, specifically how it impacted her sons and the role they played in helping their country mourn in the aftermath. “Diana, 7 Days” is set to air in September to help mark the 20 year anniversary of her death.

“Part of the reason why Harry and I want to do this is because we feel we owe it to her,” Prince William said in a statement released by the network. “I think an element of it is feeling like we let her down when we were younger. We couldn’t protect her. We feel we at least owe her 20 years on to stand up for her name and remind everybody of the character and person that she was. Do our duties as sons in protecting her.”

William’s brother, Harry, echoed those sentiments, saying, “When she died there was such an outpour of emotion and love which was quite shocking. It was beautiful at the same time, and it was amazing now looking back at it. It was amazing that our mother had such a huge effect on so many people. When you’re that young and something like that happens to you, I think it’s lodged in here, there, wherever – in your heart, in your head and it stays there for a very, very long time. I think it’s never going to be easy for the two of us to talk about our mother, but 20 years on seems like a good time to remind people of the difference that she made, not just to the Royal Family but also to the world.”

The documentary also promises interviews with family, close friends, political figures and journalists.